Agilent Technologies HP 8719D Service Manual page 325

Isolation (Crosstalk, EXF and EXR)
These are the uncorrected forward and reverse isolation error terms that
represent leakage between the test ports and the signal paths. The isolation
error terms are characterized by measuring transmission (S21, S12) with loads
attached to both ports during the measurement calibration. Since these terms
are low in magnitude, they are usually noisy (not very repeatable). The error
term magnitude changes dramatically with IF bandwidth: a 10 Hz IF bandwidth
must be used in order to lower the noise floor beyond the crosstalk specification.
Using averaging will also reduce the peak-to-peak noise in this error term.
Significant System Components.
components in the lower box are the most likely cause of isolation problems.
The transfer switch, bias tees, couplers, and samplers are the most susceptible
components.
Affected Measurements. Isolation errors affect both reflection and transmission
measurements, primarily where the measured signal level is very low. Examples
include reflection measurements of a well-matched DUT, and transmission
measurements where the insertion loss of the DUT is large.
l
Figure 11-4. Typical EXF/EXR with 3 kHz Bandwidth
1 l-1 2 Error Terms
Loose cable connections or leakage between